sterndata on "Getting rid of pop up spam windows"

We are getting unusual pop up spam windows for junk sites when you click on any of the relevant links on our site at:

http://www.teapartynation.com

The pop up windows are annoying and vary almost every time you click on a link from a new browser process. They occur using multiple ISP's and devices, including several versions of Windows and Mac OS, Linux (several builds including Knoppix, Morphix, Ubuntu and KALI) and several Samsung Galaxy tablets and phones. It is something server-side that I cannot seem to locate or determine why this is occurring at this time.

This is regardless of whether or not the end users are using pop up blockers or any anti-virus suites. It occurs in MSIE, Firefox, Chrome, Opera, Safari, Konquerer and Ice Weasel browsers.

Additionally, whenever most of our users click on link to 'continue reading' or any of the other links on the main page, many users receive a message that says:

=================================================

Error 400

We're sorry, but we could not fulfill your request for /justice-ginsburg-and-muslims-in-nice-campaign-for-trump-2/ on this server.

An invalid request was received from your browser. This may be caused by a malfunctioning proxy server or browser privacy software.

Your technical support key is: 18a8-dc9f-6992-0ee5
==================================================

FYI, I already asked the dev to disable the plugins one at a time until he finds the offending one, but so far he has been unresponsive.

I also suggested a clean install in a parallel directory, and to install the plugins one at a time until the offending plugin is located.

My final suggestion was to try installing and running this Anti-malware plugin:

https://wordpress.org/plugins/gotmls/

So far, he has been completely unresponsive and is blaming everyone except his own company and devs. This is completely unacceptable and puts the ball in my court to nail down these problems.

Where do we go from here in trying to resolve these 2 separate issues?

Thanks in advance for any tips and suggestions.

They are gratefully appreciated!

~Scot